1) Field of the Invention
The present invention relates to a retainer for a rolling bearing and the rolling bearing which do not pollute environment.
2) Description of Related Art
In a conventional rolling bearing, particularly in a ball bearing, as a metal plate for a metal retainer, an electrolytic zinc alloy-plated steel plate excellent in its rust-preventive property is used. The electrolytic zinc alloy-plated steel plate is composed of a primary surface film formed by electrolytically treating a cold rolled steel plate which is the matrix of the retainer with a treating liquid containing zinc as its main component and molybdenum, cobalt or the like and a secondary surface film formed by electrolytically treating the primary surface film with hexavalent chromate.
But the electrolytic zinc alloy-plated steel plate contains hazardous hexavalent chromium. Therefore there is a fear that in maintenance such as disassembly, inspection, cleaning, and the like of the rolling bearing, hazardous substances including the hexavalent chromium flow out of the electrolytic zinc alloy-plated steel plate and contaminate an operator and damage operator's health. Thus the electrolytic zinc alloy-plated steel plate has a problem that it pollutes environment, which makes it difficult to use it.
Restriction of Hazardous Substances order (RoHS order) restricting the use of the six specified hazardous substances contained in electric and electronic apparatuses has become effective in 15 countries affiliated with the EU (European Union). The RoHS order prohibits the use of lead, hexavalent chromium, mercury, cadmium, a bromine-based fire-retardance agent (PBB (polybromobiphenyl) and PBDE (polybromodiphenyl ether)) for about 70 electric and electronic products which will be sold in the EU member countries after July in 2006. With the effectuation of the RoHS order in Europe, in all-around electric appliance makers, there is a movement of applying the use restriction of the six specified hazardous substances which pollute environment to their products.
To solve this problem, a method of treating the surface of a metal plate which is used for a sealing device of the rolling bearing including chromating with trivalent chromium is known (patent document 1).
In many cases, the retainer for the rolling bearing and the rolling bearing are used with grease enclosed therein. Thus in many cases, the characteristic of the rolling bearing is determined by the grease enclosed therein. Therefore the suitability of the enclosed grease for the surface-treated metal member is very important. But the suitability of the enclosed grease for the chromated metal member has not been investigated.
The grease-enclosed bearing is cleaned at the time of maintenance of the rolling bearing. In cleaning the grease-enclosed bearing, there is a case in which the chromated surface layer peels off. The relationship between the chromating with trivalent chromium and the cleaning performance has not been investigated.    Patent document 1: Japanese Patent Application Laid-Open No. 2002-357227